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Bronze Birch Borers

Of the number of pests which are attracted the birch trees, the bronze birch borer (Agrilus anxius) is the most important as it is both lethal and difficult to control. As an adult, the borer is a small bronze coloured beetle up to 2 inches (5cm) in length. The damage, though, is not caused by the beetle itself but by the larvae which bore into the phloem and cambium layers after emerging from their eggs on the bark. The borers' tunneling weakens and kills trees by interrupting the flow of sap. The entire lifecycle of the borer is one year from egg to beetle.

Evidence of borer infestation is a progressive thinning of the crown of the tree beginning at the top. Trees generally die after about two or three years, that is, after two or three infestations by the larvae.

Recommended Control Steps

If caught early enough, immediately apply the Multi-Insect Killer Tree Injection Kit to the tree. This insecticide is injected directly into the tree’s vascular system and released quickly to help control insects already inside the vascular system.

To prevent repeated borer attacks and in areas of known birch borer activity, a number of steps can be taken to prevent attacks in healthy trees. In the early spring, treating the tree with the Once-A-Year Insecticidal Drench w/Merit helps protect the tree’s vascular system. This treatment can be supplemented by regularly spraying (every three to three weeks) the tree’s trunk with a good dosage of Borer-Miner Killer, thus creating a barrier to reduce further insect penetration through the bark.

The good news is that healthy, well-situated, well-maintained birches are more resistant to the borer. Females prefer to lay eggs in the sunlight and are less attracted to trees whose trunks are shaded. The insects are also attracted to tree wounds and so care should be taken to avoid damaging the bark of trees. Finally, trees under stress are more likely to be successful borer targets, so it is important to ensure that birch trees receive adequate water. To help ensure that a birch tree is healthy, apply the TreeHelp Annual Care Kit for Birch trees in the spring or early summer.

In addition, not all birch varieties are equally susceptible to the bronze birch borer. The European white birch and gray birch are considered most vulnerable, the paper or canoe birch less so, and the river birch seems to be relatively resistant.